Influenza is a leading cause of death and illness and affects the upper and lower respiratory tracts. Influenza virus causes a highly infectious respiratory illness that results in over 200,000 hospitalizations and 36,000 casualties in the US during severe seasons. Globally, 20% of children and 5% of adults develop symptomatic influenza every year (Nicholson, K. G. et al (2003) Lancet 362:1733-1745). Morbidity and mortality varies due to the virulence of the influenza strain and the host's exposure history, age, and immune status. In addition to seasonal epidemics, pandemic influenza strains emerge with some regularity. Due to the lack of pre-existing immunity against the major viral antigens, pandemic influenza can spread quickly, often with more severe disease than seasonal influenza (Swartz, K. A. & Luby, J. P. (2007) Tex Med 103: 31-34). For example, the 1918-1919 “Spanish Flu” pandemic strain was the most deadly plague of the 20th century, infecting 32% of the global population and leading to over 20 million deaths (Webster, R. G. (1999) Proc Natl Acad Sci USA 96:1164-1166). Recently, the 2009 H1N1 virus spread to 61 million people in the U.S., leading to an estimated 274,000 hospitalizations from April 2009-April 2010 (Lagace-Wiens, P. R. et al (2010) Crit Care Med 38:e1-9). This pandemic shut down schools and commercial establishments due to uncertainty how to respond to the threat.
There are three types of influenza viruses, influenza A, B and C. Human influenza A and B viruses cause seasonal epidemics of disease. Influenza type C infections cause a mild respiratory illness and are not thought to cause epidemics. Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: the hemagglutinin (H) and the neuraminidase (N). There are 17 different hemagglutinin subtypes and 10 different neuraminidase subtypes. Influenza A viruses can be further broken down into different strains. Current subtypes of influenza A viruses found in people are influenza A (H1N1) and influenza A (H3N2) viruses. Influenza B viruses are not divided into subtypes, but can be further broken down into two different lineages. Influenza A (H1N1), A (H3N2), and influenza B viruses are included in each year's influenza vaccine.
Five kinds of clinically relevant influenza viruses are circulating in the human population at the present time, three of influenza A and also two of influenza B. Influenza A type virus is divided into two distinct phylogenetic groups 1 and 2. Group 1 includes hemagglutinin subtypes H1, H2, H5, H6, H8, H9, H11, H13 and H16. Group 2 includes H3, H4, H7, H10, H15 and H14. Currently relevant circulating influenza A viruses of group 1 are of subtype H1, which is further divided into those of human and swine origin, and group 2 relevant circulating viruses are presently of subtype H3. Influenza A viruses are responsible for the bulk of seasonal disease, with H3 viruses dominating eight of the past twelve influenza seasons in the United States (CDC Seasonal flu; United States Surveillance Data). In 1968, an H3 virus caused one of the three major influenza pandemics of the twentieth century and H3 viruses have persisted since that time as a significant agent of human disease. In addition to humans, H3 influenza viruses commonly infect birds, swine, and horses. Influenza B viruses have been circulating in humans for more than 100 years, with current strains divided into two lineages, the Yamagata lineage and Victoria lineage. Recently the trivalent influenza vaccine has expanded to a quadrivalent vaccine covering both lineages of influenza B, as well as an H1 virus and H3 virus.
Current treatments for influenza are not adequate and can be ineffective. Despite widespread vaccination, susceptibility to influenza remains. The factors contributing to susceptibility include (1) incomplete vaccination coverage such as with the 2009 H1N1 pandemic, when vaccine shortages were widespread, (2) years such as 2008 when the vaccine formulation poorly represented the strains in circulation, (3) reduced efficacy of vaccination in the elderly, as the average efficacy ranges from 40-50% at age 65, and only 15-30% past age 70, and (4) the emergence of pandemic strains not represented in seasonal vaccines. Further, drug resistance against the anti-viral therapeutics currently available for the treatment of influenza has become a serious problem. Resistance to adamantanes (amantidine and rimantadine), drugs that act on the M2 protein and inhibit viral fusion, increased from 1.9% in 2004 to 14.5% during the first 6 months of the 2004-2005 flu season, and currently has surpassed 90% (Sheu, T. G. et al (2011) J Infect Dis 203:13-17). Resistance to Tamiflu, an antiviral drug that inhibits the influenza neuraminidase protein, dramatically increased from 1-2% of H1N1 viruses during the 2006-2007 flu season, to 12% by 2007-2008, and exceeded 99% of the seasonal H1N1 viruses in 2009. Fortunately, the pandemic H1N1 strain of 2009 was sensitive to Tamiflu and likely resulted in fewer deaths during the pandemic. As such there is an overwhelming need for new influenza therapeutics.
The development of therapeutic antibodies for influenza is gaining attention as conserved epitopes within the hemagglutinin (HA) molecule have recently been discovered. There have been several reports of the isolation and characterization of human monoclonal antibodies (MAb) capable of recognizing and neutralizing a diverse number of influenza A virus subtypes. Many of these are targeted to the hemagglutinin (HA) glycoprotein, which elicits the most robust neutralizing antibodies during vaccination or natural infection. HA is composed of two subunits HA1 and HA2 which are critical components in virus infection. HA1 is involved in attachment to the host cell receptor sialic acid and HA2 mediates fusion of viral and endosome membranes. MAb CR6261 is a well characterized antibody that binds to H1 viruses and other subtypes (H5) within group 1 and binds on the HA2 subunit (Throsby M et al (2008) PLoS ONE 3:e3942; Eckert D C et al (2009) Science 324:246-251; Friesen R H E et al (2010) PLoS ONE 5(2):e1906; U.S. Pat. No. 8,192,927). MAb CR8020 binds to the membrane-proximal region of HA2 on both H3 and another subtype (H7) viruses which are group 2 viruses (Eckert D C et al (2011) Science 333:843-850). The antibody FI6v3 from researchers in Switzerland can bind to an epitope present on both group 1 (H1) and 2 (H3) viruses, however FI6 has shown limited efficacy in mice (Corti D et al (2011) Science 333:850-856). Palese and colleagues have reported broadly protective monoclonal antibodies against H3 influenza viruses using sequential immunization in mice with different hemagglutinins (Wang T T et al (2010) PLoS Pathog 6(2):e1000796; US Application 20110027270). Using this approach, a broadly reactive H1 antibody was isolated (Tan G S et al (2012) J Virol 86(11):6179-6188).
Currently, the usual antibody therapy doses are well-established to be multiple mg/kg per dose, based on research and clinical experience to date with numerous recombinant antibodies, including the over twenty monoclonal antibodies that have been clinically approved in the United States (Newsome B W and Ernstoff M S (2008) Br J Clin Pharmacol 66(1):6-19). For example, panitumumab, an anti-EGFR fully human antibody approved for colorectal cancer, is administered intravenously at 6 mg/kg over 1-1½ hours every 2 weeks. Using an average human weight of 70 kg, this amounts to 420 mg of antibody per dose.
No monoclonal antibody has yet been clinically approved for influenza. Reports of studies with influenza antibodies in animals demonstrate that the effective dose range of these antibodies when given intravenously or intraperitoneally for therapeutic or prophylactic purposes require ranges from 1 mg/kg up to 100 mg/kg. Phase I clinical trials in the US with some of these antibodies (CR6261, CR8020, TCN-032) use a dose escalation in safety and tolerance studies from 2 mg/kg up to 50 mg/kg (clinicaltrials.gov; NCT01390025, NCT01406418, NCT01756950). This large amount of material presents a major hurdle in the development of this new line of antibody therapeutics. Specifically, systemic doses in this range results in a significant cost of material and also time and personnel costs involved in infusions. As such there is an imperative need to either increase efficacy and/or reduce the amount of material needed for antibody therapy or prophylaxis against influenza to be a viable alternative.
The citation of references herein shall not be construed as an admission that such is prior art to the present invention.